LTE (Long Term Evolution) is a radio access technology standardized by 3GPP (3rd Generation Partnership Project). Only the Packet Switched (PS) domain is supported by LTE, i.e. all services are supported in the PS domain. The standard is based on OFDM (Orthogonal Frequency Division Multiplexing) in the downlink and SC-FDMA (Single Carrier Frequency Domain Multiple Access) in the uplink.
In LTE, no dedicated transport channels are used for traffic. Instead, shared transport channels are used in both downlink and uplink. These shared transport channels, DL-SCH (Downlink Shared Channel) and UL-SCH (Uplink Shared Channel), are each controlled by a scheduler that assigns different parts of the downlink and uplink shared channels to different UEs (User Equipments) for reception and transmission respectively.
In the uplink, the UL-SCH is mapped to a Physical Uplink Shared Channel (PUSCH). Resource usage in the Physical Uplink Shared Channel is very tight and it would be beneficial if it were to be possible to somehow find free resources that could be used for additional control signalling or user data.